Burner for flame photometers



April 1970 J. D. KELLER 3,507,589

BURNER FOR FLAME PHOTOMETERS Filed Dec; 2, 1966 JOHN D. KELLER INVENTOR.

ATTORNEY United States Patent 3,507,589 BURNER FOR FLAME PHOTOMETERS John D. Keller, Greece, N.Y., assignor to Bausch & Lomb Incorporated, Rochester, N.Y., a corporation of New York Filed Dec. 2, 1966, Ser. No. 598,736 Int. Cl. Bb 7/06; G01n 21/00; Gilli 3/00 US. Cl. 431-126 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to atomizing burners for producing a flame whose spectrum is characteristic of a sample solution being atomized wherein a sample tube employed to convey the sample solution to be atomized is formed with a short first portion having a passage therethrough of capillary size and a substantially longer second portion having a passage therethrough substantially greater than capillary size. The sample tube is surrounded by another tube which conveys combustion supporting gas toward the flame zone. The gas flowing past the output portion of the sample tube atomizes the sample solution into the flame zone. The lengths of the sample and gas supporting tubes, measured in the direction of sample and gas flow, areat least four times their width measured normal to the direction of flow.

In the atomizing burners of the prior art, a sample tube is generally included in the burners to convey a solution to be atomized in a flame zone and analyzed. Such sample tubes includes a continuous capillary sized passage from end to end. It was found that a burner including a sample tube formed with such a continuous capillary size passage generally required frequent cleaning and/or a substantial stabilizing period of operation before a reading could be accurately taken. For example, if a non-aqueous solution, such as a protein solution is tested, the protein solutioncoats the inner surfaces of the capillary sized tube so that the apparent impedance of the passage changes as a result of the interaction of the solution and the coating. The formation of the protein coating is a relatively slow process so that impedance of the capillary tube varies slowly until an equilibrium point is reached. Accordingly, a waiting period is generally required so that the flow through the burner is stabilized before a reading can be accurately taken. In addition, the flow rate of the sample solution through the continuous capillary sized sample tube was found to vary according to the composition of the solution tested. If the spectrophotometric instrument employing the burner was originally calibrated with an aqueous solution, and tests were made on non-aqueous solutions, a subsequent recheck on the calibration indicate that the flow of the aqueous standard solution had changed due to the coating within the capillary sized passage. As a result, the change in flow rate varies the testing conditions from sample to sample depending upon the sample solution composition and accordingly introduc s an undesirable error in the measurements. Furthermore, the second calibration made with an aqueous solution after testing a non-aqueous solution changes slowly until the tube is flushed clear of the coating. Therefore, the continuous capillary sized passage must be frequently cleaned with a brush or wire or flushed until the coating on the Walls of the tube is removed. This requires a considerable downtime or waiting period for the apparatus each time the calibration is to be made, or solutions of different compositions are to be tested.

It is therefore an object of this invention to provide a new and improved atomizing burner for flame photometers and the like.

It is also an object of this invention to provide a new and improved atomizing burner that effectively atomizes aqueous and non-aqueous solutions without requiring a period of stabilization or cleaning between tests and calibration checks.

BRIEF SUMMARY OF THE INVENTION The invention of this application comprises an improved sample tube for atomizing burners for spectrophotometric apparatus and the like. The sample tube comprises a short first portion formed with a passage there through of substantially capillary size and a substantially longer second portion having a passage therethrough of substantially greater size than capillary size. The second portion of the sample tube is adapted to be connected to a source of sample solution to be atomized.

The sample tube is mounted within a burner having a first tube formed with an inlet receiving fuel gas and an output end for directing a flow of fuel gas toward a flame zone, and a second tube formed with an inlet for receiving a pressurized combustion supporting gas and an outlet end symmetrically positioned with respect to the first tube outlet end for directing a flow of combustion supporting gas toward the flame zone and mixing with the fuel gas to form a combustible mixture. The sample tube is mounted within the burner to extend through the second tube so that the first portion of the sample tube extends through the output end of the second tube to form an orifice type gas passage for the flow of the combustion supporting gas. The flow of the combustion supporting gas through the gas passage atomizes the sample solution into the flame zone. The use of the sample tube of the invention having the second elongated portion with a passage substantially greater than capillary size allows the free flow of aqueous and non-aqueous solutions through the sample tube for atomizing in the flame zone without introducing noticeable instabilities in the flow rate due to coatings forming within the sample tube.

The novel features which are considered to be characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization, and method of operation as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings in which:

FIG. 1 is an illustration of a portion of a flame photometer including the atomizing burner of the invention:

FIG. 2 is a cross-sectional view of the burner in FIG- URE 1;

FIG. 3 is an enlarged cross-sectional view of the top port on of the burner in FIGURE 2; and

FIGURE 4 is an enlarged top view of the center of the burner of FIGURE 3 as viewed from lines 44.

The portion of the flame photometer illustrated in FIG- URE 1 includes a chimney 10 surrounding a burner 12 including the invention. The burner 12 has a first input tube 14- adapted to be connected to a source of fuel gas and a second input tube 16 adapted to being connected to a source of combustion supporting gas such as oxygen or a. mixture of fuel gas and oxygen. A sample tube 18 extends through the bottom of the burner 12 and has a flexible extension 19 adapted to be inserted into a container 20 including a sample solution to be tested. The chimney 10 includes a conventional radiation transparent portion or lens 22 through which the spectrum of the flame 23 generated by the burner 12 can be observed.

Referring now to FIGURES 2-4, the burner 12 includes an outer body or tube 30 formed with a cylindrically shaped outer gas chamber 32 connected through an input passage 34 to the fuel gas inlet tube 14. An inner cylindrically shaped gas chamber 36 is formed by a tube 38 which is coaxially aligned with the outer chamber 32 and extends through the outer body 30 for connection through an inlet passage 40 to the combustion supporting gas input tube 16. The gas chamber 32 is partially closed at its upper end by a ring shaped plate 42 leaving a small ring shaped opening 44 through which the pressurized fuel gas flows. A cone shaped cap 46 formed with an opening 48 directs the fuel gas from the chamber opening 44 through the opening 48 toward a flame zone (above the dashed line 50). The cap 46 is resiliently held in place by an O ring 47.

The sample tube 18 extends coaxially through the center of the inner chamber 36. The sample tube 18 includes an upper or output portion 52 of reduced size formed with an opening or passage 54 therethrough of substantially capillary size, and a substantially longer or elongated portion 56 extending through an opening 60 in the bottom of the inner chamber 36 having a passage 62 therethrough substantially greater than capillary size. Typically, the diameter of the passage 54 through the output end 52 is in the order of 0.3 mm. while the diameter of the passage 62 through the portion 56 in the order of 1.0 mm. The sample tube portion 56 is connected to the tube 19 for receiving the sample solution. In addition, the length of output portion 52 of sample tube 18 should, to achieve uniform flow of the sample conveyed therewithin, be at least four times greater than its width.

The upper end of the inner chamber 36 is enclosed by a cap 64, having a cylindrical passage 66 extending therethrough. The sample tube 18 is positioned within the inner chamber 36 so that its reduced output end 52 is coaxially aligned with the passage 66 providing a limited tubular shaped outlet gas passage for the combustion supporting gas received within the inner chamber 36. The gas passage 66 is of sufiicient length to approach a uniform flow of the combustion supporting gas flow. The length of the passage 66 (measured in the direction of the gas flow) should be at least four times its width (measured normal to the direction of gas flow) to approach a uniform flow. In addition, the output portion 52 of sample tube 18 should be formed with an internal diameter at least onefourth of the length of gas passage 66 for the same reason. The upper portion of the passage 66 is bevelled to shape the flow of combustion supporting gas through the opening 48. The output end 52 of the sample tube 18 is held in place by four support members 70 extending from the cap 64. The support members are made thin and are located at the bottom of the passage 66 so as to minimize their turbulent producing eflect on the flow of gas through the gas passage 66.

The gas passage 66 effectively acts as an orifice wherein the pressurized combustion supporting gas applied to the inner chamber 36 is exhausted through the gas passage 66 at a high velocity providing a venturi type effect for inducing flow of the sample solution through the tube 18 from the container 20 and atomizing the solution into the flame zone above the dashed line 50'. The walls ofv output portion 52 of the sample tube should be as thin as possible to provide eflici-ent coupling between the capillary passage 54 and the gas passage 66 and still provide a substantially rigid structure that can take the abuse of cleaning when necessary. The rapid flow of combustion supporting gas through the opening 48 effectively mixes it witth the fuel gas to provide a combustible mixture that burns with a spectral characteristic determined by the solution being atomized.

The sample tube 18, as disclosed, was found to overcome the objections to the continuous capillary sized burner sample tubes of the prior art. For example, any coating deposited on the inner walls of the sample tube on the elongated portion 56 has little effect on the burner operation. The output portion 52 of the sample tube does not build up a coating that noticably impedes the flow of sample solution. Substantially the same flow is exhibited by non-aqueous solutions as is exhibited by aqueous solutions thereby providing for more accurate sample testing. Furthermore, it was found that the burner with the same tube 18 did not effectively require a stabilization period of operation to provide an even sample solution flow. Tests are able to be conducted by simply inserting the tube 19 into the container 20. In addition to the foregoing, the apparatus used with the burner including the invention can be calibrated with an aqueous solution, a series of tests made on non-aqueous solutions and the apparatus subssequently rechecked for calibration with the aqueous solution Without cleaning .or flushing the sample tube, or requiring a stabilization period of operation. It was also found that a burner including the same tube 18 was not as sensitive to noise and to particles in the solution as were the continuous capillary sized tubes of the prior art. By using a sample tube with the capillary and larger than capillary sized passages as previously set forth, the interaction length of the tube to particles in the sample solution was reduced so that they did not notably impede the flow of the sample solution. The lower impedance sample tube of the invention provides a uniform flow of atomized sample solution into the flame zone Without introducing an expected and undesirable dribble or large droplet effect. Furthermore, it was found that the burner With the sample tube of the invention is capable of operating under laboratory condition for at least a period of one week without cleaning or flushing.

What is claimed is:

1. In an atomizing burner for spectrophotometric apparatus having a first tube formed with an inlet for receiving fuel gas and an output end for directing a flow of fuel gas toward a flame zone and a second tube extending through said first tube formed with an inlet for receiving pressurized combustion supporting gas and an output and coaxially positioned with respect to said first tube output end for directing a flow of said combustion supporting gas toward said flame zone for mixing with said fuel gas to form a combustible mixture, the improvement comprising:

a sample tube comprising an output portion formed with a passage therethrough of capillary size and a substantially longer inlet portion formed with a passage therethrough of substantially greater size than capillary size for connection to a source of sample solution to be atomized, and

means for mounting said sample tube in said burner so that said sample tube extends through said second tube, and said output portion of said sample tube extends through said output end of said second tube to form an orifice type gas passage for said combustion supporting gas for atomizing said sample solution into said flame zone in response to said pressurized combustion supporting gas applied to said second tube.

2. The improvement as defined in claim 1 wherein the length of said passage in said output portion of said sample tube is at least four times greater than the width of said passage.

3. The improvement as defined in claim 1, wherein said output portion of said sample tube and said output end of said second tube form a tubular shaped gas passage for the flow of said combustion supporting gas toward said flame zone, the length of said tubular shaped gas passage measured along the direction of gas flow being at least four times the dimension of the gas passage normal to the length of said gas passage.

4. In an atomizing burner for spectrophotometric apparatus having a first tube formed with an inlet for receiving fuel gas and an output end for directing a flow of fuel gas toward a flame zone and a second tube extending through said first tube formed with an inlet for receiving pressurized combustion supporting gas and an output end coaxially positioned with respect to said first tube output end for directing a flow of said combustion supporting gas toward said flame zone for mixing with said fuel gas to form a combustible mixture, the improvesaid circular tubular gas passage having a length, measment comprising: ured along the direction of gas flow, at least four a sample tube comprising an output portion formed times the radial dimension of the gas passage normal with a cylindrical passage therethrough a capillary to the gas flow, and

size and a substantially longer inlet portion formed said output portion of said sample tube having an in- With a passage therethrough of substantially greater 5 ternal diameter at least one fourth the length of said size than capillary size for connection to a source gas passage.

of sample solution to be atomized, said sample tube References Cited output portion having a substantially cylindrical ex- UNITED STATES PATENTS ternal shape and said second tube being formed with 10 a substantially cylindrical opening having a diam- 3,298,785 1/1967 Relll 35687 eter greater than the external diameter of said output 2,532,687 12/1950 wFlchselbaumportion, and means for mounting said sample tube 2,714,833 8/1955 Gllbertin said burner so that said sample tube extends con- 2,845,334 7/1958 Brafie at centrically through said second tube and said out- 15 3:267699 8/1966 Kmseleyput portion of said sample tube extends through said 3,284,163 11/1956 Deal output end of said second tube to form a circular tubular gas passage therebetween for said combus- RONALD L-WILBERTPnmarY Exammer tion supporting gas for atomizing said sample solu- F, L, EVANS, A i t nt Examiner tion into said flame zone in response to said pres- 20 surized combustion supporting gas applied to said US. Cl. X.R.

second tube, 239424; 35687 

